1. Field of the Invention
The present invention relates to a process for forming a metallic workpiece by pressurizing, process which can attain favorable pressurizing-and-forming characteristics. Moreover, it relates to a pressurized-and-formed member which is produced by the pressurizing forming process.
2. Description of the Related Art
Plastic processing has been carried out in order to make metallic workpieces into desired shapes or have the resulting metallic articles show good characteristics in terms of the strength, and so forth, by pressurizing and forming. For example, it is possible to name the following: forging which is carried out while a metallic mass is placed on a die; re-compressing which is carried out in order to highly densify sintered members, in order to give a high accuracy thereto, or the like; coining; and sizing; and moreover rolling in which rollers are used, as well as extruding in which dies are used, drawing or forming by rolling, and so on.
In the meantime, when such pressurizing forming processes are carried out, a high pressure is exerted to the contact surface (or the pressurized-and-contacted interface) between a forming tool, such as dies, rollers, dies, and the like, and a metallic workpiece. Accordingly, in order to attain favorable pressurizing-and-forming characteristics by inhibiting the seizure, etc., between the forming tool and the metallic workpiece, it is necessary to securely give a lubricative characteristic, which can withstand the high pressure, and so forth, to the pressurized-and-contacted interface.
As for such a lubricating method, the following have been carried out conventionally. For instance, in an oil lubricating method, an oil is applied onto a surface of a metallic workpiece or a forming surface of a die, and so forth, by spraying, or the like. In a chemical conversion treatment (e.g., the Bonde treatment (trade name)), a phosphate film is formed on a surface of a metallic workpiece or a surface of a die, and the like. Moreover, when a metallic workpiece is small relatively, it has been often carried out so that a dried lubricant powder is applied on a surface of the metallic workpiece. The lubricant powder is made from zinc stearate (hereinafter abbreviated to as “ZnSt.”), and so on. The applying operation is carried out in the following manner. The metallic workpiece and the lubricant powder are charged into a tumbling barrel, and the lubricant powder is applied on the metallic workpiece by the tumbling action.
However, when the oil lubricating method or the chemical conversion treatment is carried out, it has been required to spend much expenses to disposed of the waste fluids. In particular, since the environmental regulations have become strict recently, the processing methods are not a preferable lubricating method at all, processing methods which discharge waste fluids making large environmental loads.
Moreover, when the oil lubricating method is carried out, the working environment deteriorates due to the adhesiveness, and so forth, on the resultant formed articles, and accordingly it is necessary to additionally carry out a degreasing step. In addition, when the forming allowance (or the ironing allowance) is large, the oil lubricating method cannot attain a sufficient lubricative characteristic so that it results in the damages to dies, or the like, and in lowering the longevity thereof.
When the chemical conversion treatment is carried out, it is possible to attain a favorable lubricative characteristic. However, it is necessary to carry out a pre-treatment step, etc., and is required to spend high film processing costs for preparing a lubricating film. Moreover, when the chemical conversion treatment is carried out, it is needed to control the waste fluids much stricter than it is needed in the oil lubricating method. Accordingly, the chemical conversion treatment is not preferable in view of the man-hour requirements and the processing costs.
In addition, the method in which the lubricant powder is applied on a surface of a metallic workpiece is not practical at all, because the method is applicable limitedly to cases where metallic workpieces are small-sized articles, and because it is further necessary to additionally carry out a tumbling step, and so forth.